Diverse apparatus have been developed for keeping the windshields and rear windows of automobiles clear of fog. Today, electric blowers or are commonly used for clearing windshields. Electric resistance heaters, secured to the rear window, are employed for removing condensation therefrom.
Manually-operated switches are usually provided so that the operator of an automobile can energize the usual blower and resistance heater when needed. The drain on the automobile battery therefore continues until the operator deenergizes the defogging apparatus which may be a long time after the windshield and rear window are free of fog. This continuing drain can reduce the performance of the battery, blower and resistance heater. Gasoline consumption of the automobile is also adversely impacted.